1. Field of the Invention
The invention relates to vehicle axle/suspension systems, and in particular to the suspension assemblies of those systems which are useful for heavy-duty vehicles such as trucks and tractor-trailers. More particularly, the invention is directed to a heavy-duty trailing or leading arm rigid beam-type suspension assembly for trucks and tractor-trailers, in which the axle is securely and efficiently connected to the beams by an improved U-bolt bracket/axle seal. The improved U-bolt bracket/axle seal, together with the manner in which the axle-to-beam connection is assembled, increases weld fatigue life and increases durability of the axle at or near the axle-to-beam connection. More specifically, this is accomplished by providing a structure whereby certain loads imparted on the axle-to-beam connection during operation of the vehicle are shared between the U-bolt bracket/axle seat, the welds used to attach the axle to the U-bolt bracket/axle seat, and the beam, and by optionally placing these welds in a residual compressive stress field on the axle.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Air-ride trailing and leading arm spring beam-type axle/suspension systems also are often used in the industry. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The opposite end of each beam also is connected to a bellows air spring or its equivalent, which in turn is connected to a respective one of the main members. A brake assembly and one or more shock absorbers also are mounted on each of the beams and/or axle. A height control valve is mounted on the hanger and is operatively connected to the beam in order to maintain the ride height of the vehicle. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The beam on which the axle is mounted is typically either a top-mount/overslung beam or a bottom-mount/underslung beam. An axle is mounted on the top of and is supported by the bottom-mount/underslung beam-type, with generally an upper portion of the axle being exposed. Welding alone typically is inadequate to maintain the integrity of the rigid axle-to-beam connection for both bottom-mount/underslung and top-mount/overslung beams due to certain loads to which the axle-to-beam connection is subjected during vehicle operation. Therefore, both bottom-mount/underslung and top-mount/overslung axle-to-beam mounts are fortified in some manner to maintain the mount integrity and prevent separation of the axle from the beams. Such fortification usually includes additional mounting hardware such as U-bolts, U-bolt brackets/axle seats, welds, and the like, resulting in a secure axle-to-beam connection more capable of withstanding operational loads.
However, even with such fortification, these prior art axle-to-beam connections can still potentially exhibit less than optimal fatigue life of the weld between the axle and the U-bolt bracket/axle seat as well as less than optimal durability of the axle itself at or near the axle-to-beam connection. This can potentially occur because the loads acting on the axle are transferred almost entirely through the weld that attaches the U-bolt bracket/axle seat to the axle.
Therefore, a need exists in the art for an axle-to-beam connection for axle/suspension systems, which utilizes an improved axle-to-beam connection whereby certain loads imparted on the axle-to-beam connection during operation of the vehicle are shared between the U-bolt bracket/axle seat, the weld, and the beam. A need also exists in the art for an axle-to-beam connection for axle/suspension systems, which replaces the known prior art U-bolt bracket/axle seat, that changes the location of certain welds relative to the axle and the U-bolt bracket/axle seat, and that optionally places the welds generally within a residual compressive stress field created on the axle. As a result of sharing loads between the U-bolt bracket/axle seat, the weld and the beam, and optionally locating the welds generally within a residual compressive stress field, the axle-to-beam connection reacts loads belter than known prior art axle-to-beam connections, increases the fatigue life of the welds of the axle-to-beam connection and increases durability of the axle at or near the axle-to-beam connection, resulting in a longer life axle-to-beam connection.